Conventional computers work by manipulating bits that exist in either a 0 state or a 1 state. In contrast, quantum computers encode information as quantum bits, or qubits, which can exist in 0 state, 1 state or a superposition of 0 and 1 states. In other words, qubits can be both 0 and 1 (and all points in between) at the same time. Qubits can be represented by atoms, ions, photons or electrons and their respective control devices that are working together to act as computer memory and a processor.
The superposition of qubits can give quantum computers inherent parallelism and allow a quantum computer to work on a large number of computations at once, while conventional computers work on one computation at a time. For example, a 30-qubit quantum computer can equal the processing power of a conventional computer that could run at 10 teraflops (trillions of floating-point operations per second). As a comparison, today's typical desktop computers run at speeds measured in gigaflops (billions of floating-point operations per second).
Quantum computers can also utilize another aspect of quantum mechanics known as entanglement, which can enables making measurement of the qubits indirectly to preserve their integrity (i.e., without changing their values). In quantum physics, if an outside force is applied to two atoms, the outside force can cause the two atoms to become entangled, and the second atom can take on the properties of the first atom. If left alone, one atom will spin in all directions. Once disturbed, one atom chooses one spin, or one value. At the same time, the second entangled atom chooses an opposite spin, or value. Therefore, the properties of one atom in an entangled pair can be derived by measuring the properties of the other atom in the entangled pair. This method avoids any direct measurement of the atom of interest, thereby avoiding changing or destroying the value of the qubit due to measurement.